WO2022148770A1

WO2022148770A1 - Heating device

Info

Publication number: WO2022148770A1
Application number: PCT/EP2022/050138
Authority: WO
Inventors: Manfred Gruber
Original assignee: Att Advanced Thermal Technologies Gmbh
Priority date: 2021-01-05
Filing date: 2022-01-05
Publication date: 2022-07-14
Also published as: EP4275452A1

Abstract

The invention relates to a heating device made of a composite film having an electrically insulating carrier film (5) and a cover film (6), wherein resistor elements as planar heating elements as well as electrodes (3) are located on the carrier film (5), wherein the electrodes (3) connect the resistor elements to connection points (4) for connecting a power supply. According to the invention, the heating elements are in the form of a plurality of heating panels (1) which are positioned next to one another on the carrier film (5) and which are each surrounded in their circumferential region by ribs (2) made of cured hot-melt adhesive, wherein the cover film (6) is fastened to the carrier film (5) by means of the ribs (2) made of cured hot-melt adhesive, and the ribs (2) made of cured hot-melt adhesive project beyond the heating panels (1) in the direction of the cover film (6). In this way, a heating device is provided in which the risk of damage to the planar heating elements under pressure is reduced, and the pressure resistance thereof is thus increased.

Description

HEATER

The invention relates to a heating device made of a film composite with an electrically insulating carrier film and a cover film, with resistance elements being arranged as flat heating elements and electrodes on the carrier film, with the electrodes connecting the resistance elements to connection points for connecting a power supply, according to the preamble of claim 1 .

Heating devices of the type mentioned are designed as flexible heaters with different structures and are used, for example, to heat electrical components such as accumulators. The charging and discharging cycles as well as the service life and the safe operation of accumulators are strongly dependent on their temperature control. For this reason, cooling devices have been proposed, for example, which consist of a film composite with a plurality of film layers, between which cooling channels are formed, into which a coolant can be introduced. The cooling device rests against the accumulator, so that the coolant flowing through the composite film cools the accumulator. The introduction of the coolant inflates the composite film somewhat, which improves the physical contact with the accumulator and thus its cooling.

Furthermore, heating devices made of a film composite are known, in which resistance elements are arranged as flat heating elements and electrodes between a carrier film and a cover film. The electrodes connect the resistance elements to connection points for connecting a power supply, so that current can flow through the resistance elements. The resistance elements represent an electrical resistance in which current is converted into heat and thus form the desired heat source in the present application. PTC resistance elements, which are also referred to as PTC thermistors, have the property of increasing electrical resistance as the temperature rises. PTC resistance elements with a highly non-linear characteristic are preferably used, the resistance of which initially increases slowly as the temperature rises, and suddenly increases at a temperature that is characteristic of the respective PTC resistance element increases. This characteristic temperature is also referred to as the switch-off temperature, because the PTC resistance element in question only has a low heating capacity when this temperature is exceeded, so that PTC resistance elements with such a non-linear characteristic curve are self-regulating and an equilibrium temperature is set during the course of use. Complex control devices such as temperature sensors, thermostats, current controllers and the like can therefore generally be dispensed with.

The ones designed as flat heating elements

However, resistance elements are sensitive to pressure, which can lead to problems both in production and in use. In the course of the production of a film composite, after the application of the flat heating elements, process steps for connecting film layers must be carried out, which take place under pressure and temperature increase, as a result of which the flat heating elements can be damaged. The planar heating elements are made, for example, from fusible pastes that can melt under pressure and temperature increase and, after the above-mentioned process step for connecting film layers, form structural defects when they harden again, which impair the function of the heating field in question.

In the application of a generic heating device, the pressure sensitivity of heating elements results in problems, for example, when used in combination with a cooling device described above, because the inflation of the film composite during the introduction of the coolant exerts pressure on the heating device and its heating elements. With each cooling process, the planar heating elements are also mechanically stressed, resulting in the risk of damage.

The aim of the invention is therefore to design a heating device with flat heating elements in such a way that the risk of damage to the flat heating elements under pressure load is reduced and their pressure stability is thus increased. These aims are achieved by the features of claim 1. Claim 1 relates to a heating device made of a film composite with an electrically insulating carrier film and a cover film, with resistance elements being arranged as flat heating elements and electrodes on the carrier film, with the electrodes connecting the resistance elements to connection points for connecting a power supply. According to the invention, it is proposed here that the heating elements are designed in the form of a plurality of heating fields lying next to one another on the carrier film, which are each framed in their peripheral area by webs made of cured hot-melt adhesive, the cover film being attached to the carrier film with the aid of the webs made of cured hot-melt adhesive and the webs made of hardened hot-melt adhesive protrude beyond the heating fields in the direction of the cover film. The embodiment according to the invention offers advantages both in the manufacture of the heating device and in the application of the heating device. In the course of manufacture, the framing webs made of hot-melt adhesive protect the heating fields after they have been applied during subsequent process steps in which pressure and heat are applied. As a rule, production will take place in such a way that the electrodes and the heating fields are first applied to the carrier film and then the cover film is attached to the carrier film, for example by lamination. According to the invention, after the heating fields have been applied, the hot-melt adhesive is applied to the carrier film in a structured manner, for example by screen printing, by leaving out the heating fields. The hot-melt adhesive can then dry briefly and thus harden. The quantity of hot-melt adhesive applied is selected in such a way that the webs of hardened hot-melt adhesive protrude beyond the heating fields. The webs thus absorb the pressure that is exerted when the cover film is subsequently attached, and thus protect the heating fields.

In addition, the amount of heat transferred to the heating fields is greatly reduced, so that thermally induced structural changes in the heating fields and undesired chemical reactions of the cover film material with the heating fields are avoided. The amount of heat introduced in the course of attaching the cover sheet is instead applied to the hot-melt adhesive, which melts and adhesively bonds to the cover film.

In the course of using the heating device, the framing webs protect the heating fields from mechanical loads, for example when used in combination with the cooling devices described above. The pressure exerted on the heating device is primarily absorbed by the webs, which thus protect the heating fields from mechanical stress.

The thickness of the carrier film and the cover film are in the micrometer range and is, for example, 25 mha. The thickness of the heating fields is also approximately of the same order of magnitude. In this case, it is sufficient if the webs protrude only slightly beyond the heating fields, for example in the range of a few micrometers.

For an optimal protective effect, it is preferably proposed that the entire surface of the webs made of hardened hot-melt adhesive facing the cover film is larger than the entire surface of the heating fields facing the cover film. The heating fields can, for example, each be designed in the form of strips and embedded in the surrounding material of the hot-melt adhesive.

A specific embodiment provides for the carrier film and the cover film to be a plastic film, for example a polyethylene terephthalate (PET) film. On the one hand, plastic foils ensure adequate electrical insulation from the electrical components of the composite foil and, on the other hand, enable very thin and flexible designs. In addition, plastics are available that can be printed, for example, using screen printing.

According to a preferred embodiment, it is therefore proposed that the resistance elements are made as PTC resistance elements from a hardened, carbon-based paste. Such pastes are commercially available and are also referred to as carbon pastes or carbon lacquer. They are particularly suitable for the execution of heating elements, as they heat up quickly when current flows through and due to the admixture suitable additives reach an equilibrium temperature in a self-regulating manner. Waxes, for example, have proven to be suitable as additives for the carbon pastes for the present invention, with the melting temperature of the waxes determining the PTC switch-off temperature, for example 42.degree. The carbon-based paste can be applied at room temperature in a viscous form to the plastic film by means of screen printing in the desired arrangement and thermally cured, as a result of which the heating device can be manufactured at low cost. In a corresponding form, it is also proposed that the electrodes are made from a hardened, silver-based paste. Such silver-based pastes are also referred to as silver paint and can be printed in a similar manner in a viscous form by means of screen printing with the desired gradient onto the carrier film, it having proved expedient to print the electrodes first and then the PTC resistance elements.

Furthermore, it is proposed that the carrier foil is designed as a laminate with an aluminum layer and that a measuring device is provided for detecting changes in capacitance between the aluminum layer and the heating fields in order to identify structural loads or damage to the foil composite. Since aluminum is a material with comparatively high electrical conductivity, capacitive properties appear between the aluminum layer and the heating fields, which can be used to detect an impact, i.e. a locally strong structural load or impairment of the foil composite. The measurement can be carried out, for example, by high-frequency PWM ("pulse width modulation") operation of the heating elements or by superimposing an AC voltage on the supply voltage of the heating elements.

The invention is explained in more detail below on the basis of exemplary embodiments with the aid of the accompanying drawings. The

Fig. 1 shows an embodiment of a heating device according to the invention, and the 2 shows a sectional view through a heating element and the surrounding webs.

Reference is first made to FIG. 1, which shows an embodiment of a heating device according to the invention with a longitudinal direction L and a transverse direction Q. FIG. The heating fields 1 running in the form of strips in the longitudinal direction L can be seen, with a large number of heating fields 1 being arranged next to one another in the longitudinal direction L and in the transverse direction Q. Webs 2 running in strips in the longitudinal direction L and transverse direction Q are formed between the heating fields 1 and separate two heating fields 1 lying next to one another when viewed in the longitudinal direction L and transverse direction Q. In the area of the two longitudinal edges of the heating device, one electrode 3a runs in each case from the first connection points 4a in the longitudinal direction L of the heating device. Another electrode 3b with the opposite polarity runs in the center of the heating device in the longitudinal direction L to a second connection point 4b.

In the exemplary embodiment shown, there are between six and nine heating fields 1 distributed over one half of the heating device in the transverse direction Q, and between ten and twelve heating fields 1 distributed in the longitudinal direction L. The number of heating fields 1 is of course dependent on the length and Width of the heater and the required heating power selected. Electrical contact is made with the heating fields 1 via the electrodes 3, for example with the aid of conductor tracks running in the transverse direction Q.

A possible structure of a heating device according to the invention will be explained with reference to FIG. According to the exemplary embodiment shown, the heating device has a layered structure made up of several layers. A lower carrier film 5 is designed, for example, as a laminate of a PET plastic film and an aluminum layer. An upper cover film 6 is designed as a PET plastic film, for example. Arranged on the side of the carrier film 5 facing the cover film 6 are PTC resistance elements which form the heating fields 1, as well as all the electrodes 3 and their traces. The electrodes 3 and their conductor tracks are made of a hardened, silver-based paste, which is applied in viscous form by means of screen printing with the desired profile to the carrier film 5 and is thermally cured.

The PTC resistance elements are made of a hardened, carbon-based paste, which is also referred to below as carbon paste and is also applied at room temperature in viscous form by means of screen printing in the desired arrangement to the carrier film 5 and is thermally cured. The electrodes 3 and the heating fields 1 can optionally be provided with a protective lacquer layer after they have been applied.

After the application of the heating fields 1 and any protective lacquer layer, a hot-melt adhesive, which is also known as "hotmelt", is applied in viscous form by means of screen printing with the desired course. The heating fields 1 are left out and only the areas between the heating fields 1 are covered In this way, webs 2 are formed between the heating fields 1. The amount of hot-melt adhesive applied is chosen such that the webs 2 made of hardened hot-melt adhesive protrude beyond the heating fields 1 in the direction of the cover film 6, as can be seen in Figure 2 In a final process step, the cover film 6 is attached using pressure and heat, with the hot-melt adhesive melting due to the amount of heat introduced and adhesively connecting to the cover film 6 .

Furthermore, connection surfaces 7 for temperature sensors can be seen in FIG. 1 . These connection surfaces 7 can be provided in the electrode pattern and can be produced with the application of the electrodes 3 using the screen printing process. The connection surfaces 7 are used to connect temperature sensors for monitoring the temperature of the heating device.

If an AC voltage is applied to the electrodes 3, a current flows through the conductor tracks of the electrodes 3, which is converted into heat in the PTC resistance elements of the heating fields 1, which first heats the PTC resistance elements and then the entire film composite. Of the Foil composite can thus be used as a heating device, for example for temperature control of accumulators. The design of the heating device as a composite film has the advantage that it can be applied to the cells of the accumulator and thus tolerances of the cells can be compensated for more easily. This significantly improves the heat transfer from the heating device to the cells, and additional measures such as heat-conducting pastes or thermal pads become superfluous. The invention is particularly suitable for application to cooling circuits that consist of film material and expand when coolant flows through them and thus optimally adapt to the surface of the battery cells, whereby the above-described effect of contact with the cells is utilized. This property is particularly advantageous in so-called pouch cells, which have a cambered surface due to their design and deform during operation or as they age.

The invention preferably, but not exclusively, uses carbon pastes with a PTC effect as the heating-active layer. PTC resistance elements have the advantage that the active heating of the heating elements is interrupted at a defined target temperature of e.g. 42°C by a rapid increase in the electrical resistance of the material without the need for electronic control, a fuse or any other form of overheating protection. This rules out the possibility of the heating element burning out. After the heating element has cooled down, the electrical conductivity is restored and the heating element resumes its function.

When applied to battery cells, high pressures sometimes occur during the manufacturing process. High pressures can also be observed when inflating a cooling circuit made of a foil composite material to which a heating device has previously been applied. These pressures can lead to damage to the heating panels 1, particularly if they occur simultaneously with high temperatures, since the carbon pastes used are sometimes sensitive to pressure and temperature and can melt. This can lead to functional impairments, loss of function and short circuits. The invention avoids these undesired effects by applying a layer of hot-melt adhesive to the heating layer, this application being structured using the screen printing process, so that the carbon fields are recessed and framed by webs 2 made of hot-melt adhesive, the height of which exceeds the thickness of the carbon layer of the heating fields 1.

In the subsequent manufacturing processes and during operation, compressive forces are thus absorbed by the layer of hot-melt adhesive, and mechanical loading of the heating fields 1 can be avoided. Furthermore, the printed hot-melt adhesive layer prevents the PTC layer from flowing across the width. The heating-active layer retains its function both during production of the heating device when the cover film 6 is laminated on and during operation. In addition to the protective function for the heating-active layer, the hot-melt adhesives also produce the necessary connection with the cover film 6 . Furthermore, a protective lacquer layer can optionally be printed on the PTC layer formed by the heating fields 1 in order to increase the resilience of the PTC layer at high pressures and temperatures.

If the carrier film 5 is present as a laminate with an aluminum layer, the change in the capacitance of the heating layer formed by the heating fields 1 with respect to the aluminum layer can be used to detect an impact. The measurement can be carried out by high-frequency PWM operation of the heating layer or by superimposing an AC voltage on the supply voltage of the heating layer.

A heating device is thus realized in which the risk of damage to the flat heating elements under pressure is reduced and their pressure stability is thus increased.

Claims

Patent Claims:

1. Heating device made of a film composite with an electrically insulating carrier film (5) and a cover film (6), with resistance elements as flat heating elements and electrodes (3) being arranged on the carrier film (5), with the electrodes (3) containing the resistance elements with connection points (4) for connecting a

Connect the power supply, characterized in that the heating elements are designed in the form of a plurality of heating fields (1) lying next to one another on the carrier film (5), which are each framed in their peripheral area by webs (2) made of hardened hot-melt adhesive, the cover film (6) being the webs (2) made of cured hot-melt adhesive are attached to the carrier film (5) and the webs (2) made of cured hot-melt adhesive protrude beyond the heating fields (1) in the direction of the cover film (6).

2. Heating device according to claim 1, characterized in that the entire surface of the webs (2) made of hardened hot-melt adhesive facing the cover film (6) is larger than the entire surface of the heating fields (1) facing the cover film (6).

3. Heating device according to claim 1 or 2, characterized in that it is a plastic film in the carrier film (5) and the cover film (6).

4. Heating device according to one of claims 1 to 3, characterized in that the resistance elements are made as PTC resistance elements from a hardened, carbon-based paste.

5. Heating device according to one of claims 1 to 4, characterized in that the electrodes (3) are made of a hardened, silver-based paste.

6. Heating device according to one of claims 1 to 5, characterized in that the carrier film (5) is designed as a laminate with an aluminum layer and a measuring device for detecting changes in capacitance between the aluminum layer and the heating fields (1). Detection of structural loads or damage to the composite film is provided.

7. Accumulator with a heating device according to one of claims 1 to 6.